Knock, knock, knock “Penny?”...Who doesn't love Sheldon Cooper's obsessive-compulsiveness and borderline neurotic way of knocking on Penny's door. Sheldon when needing some advice from his neighbor Penny from across the hall, always knocks on her door with the classic “Penny” call after 3 knocks calling her name each time. But you better let him finish before you answer because Sheldon doesn't like anything to break his routine. This royal blue cotton t-shirt will not only provide comfort, but an awesome Sheldon Cooper classic quote style!!!